A case of an antenna device installed on a vehicle roof is painted in a color so as to match with a body color of a vehicle in many cases. Therefore, vehicle manufacturers have to store antenna devices for respective colors in a vehicle assembly line stock, resulting in taking up a space for stock. As a countermeasure against it, double-case structure has hitherto been attempted to be provided to the antenna device. For example, an antenna unit, which is disclosed in Patent Literature 1, includes an antenna element housed water-tightly in a space formed by a base and an inner case, and is configured to cover the inner case with an outer case having a color matched with a body color.
On the other hand, in view of design, there has recently been proposed an antenna device including a case formed in a streamline shape called “shark fin”. However, under regulations on projections from vehicles, a height of the antenna device projecting from the vehicle roof is limited to about 70 mm or smaller. In the antenna device configured to receive AM/FM bands, the antenna element is required to be arranged at a position as high as possible so as to ensure electrical performance. Thus, under a condition in which the height is limited to about 70 mm or smaller, the electrical performance cannot be sufficiently ensured. As a measure for solving the problem described above, for example, a small-height type antenna device disclosed in Patent Literature 2 is designed to set an area of the antenna element to be housed within a small space as large as possible, and to arrange the antenna element at a high position. Specifically, after an antenna board with an antenna pattern formed thereon is installed upright on the base, a top portion is arranged to extend across the antenna board so that the top portion and the antenna pattern may form a complex type antenna element.